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High-quality, consistent documentation for astronomy code is one of
the major goals of the Astropy Project. Hence, we describe our
documentation procedures and rules here. For the astropy core
project we try to keep to these as closely as possible, while the
standards for affiliated packages are somewhat looser.
(These procedures and guidelines are still recommended for affiliated
packages, as they encourage useful documentation, a characteristic
often lacking in professional astronomy software.)

This section describes the standards for documentation format affiliated
packages that must follow for consideration of integration into the core
module, as well as the standard Astropy docstring format.

All documentation should be written use the Sphinx documentation tool.

The template package will provide a recommended general structure for
documentation.

Docstrings must be provided for all public classes, methods, and functions.

Docstrings will be incorporated into the documentation using a version of
numpydoc included with Astropy, and should follow the Astropy Docstring Rules.

Examples and/or tutorials are strongly encouraged for typical use-cases of a
particular module or class.

Any external package dependencies aside from NumPy, SciPy, or Matplotlib
must be explicitly mentioned in the documentation. They should also be
recorded in the pip-requirements-doc file in the root of the astropy
repository.

Configuration options using the astropy.config mechanisms must be
explicitly mentioned in the documentation.

A custom Sphinx HTML theme is included in the astropy-helpers package.
This allows the
theme to be used by both Astropy and affiliated packages. This is done by
setting the theme in the global Astropy sphinx configuration, which is imported
in the sphinx configuration of both Astropy and affiliated packages.

A different theme can be used by overriding a few sphinx
configuration variables set in the global configuration.

To use a different theme, set 'html_theme' to the name of a desired
builtin Sphinx theme or a custom theme in package-name/docs/conf.py
(where 'package-name' is “astropy” or the name of the affiliated
package).

To use a custom theme, additionally: place the theme in
package-name/docs/_themes and add '_themes' to the
'html_theme_path' variable. See the Sphinx documentation for more
details on theming.

Additional custom themes can be included in the astropy source tree by
placing them in the directory astropy/astropy/sphinx/themes, and
editing astropy/astropy/sphinx/setup_package.py to include the theme
(so that it is installed).

Astropy-helpers includes a number of sphinx extensions (some via the
sphinx-automodapi package) that are used in Astropy and its affiliated
packages to facilitate easily documenting code in a homogeneous and readable
way. The two main extensions are automodapi for
generating module documentation and automodsumm for
generating tables of module objects. Please see their documentation about
usage.

It adds links associated with each docstring that go to the
corresponding view source page on Github. From there, the user can
push the “Edit” button, edit the docstring, and submit a pull request.

It has the following configuration options (to be set in the project’s
conf.py):

edit_on_github_project

The name of the github project, in the form
“username/projectname”.

edit_on_github_branch

The name of the branch to edit. If this is a released version,
this should be a git tag referring to that version. For a
dev version, it often makes sense for it to be “master”. It
may also be a git hash.

edit_on_github_source_root

The location within the source tree of the root of the
Python package. Defaults to “lib”.

edit_on_github_doc_root

The location within the source tree of the root of the
documentation source. Defaults to “doc”, but it may make sense to
set it to “doc/source” if the project uses a separate source
directory.

edit_on_github_docstring_message

The phrase displayed in the links to edit a docstring. Defaults
to “[edit on github]”.

edit_on_github_page_message

The phrase displayed in the links to edit a RST page. Defaults
to “[edit this page on github]”.

edit_on_github_help_message

The phrase displayed as a tooltip on the edit links. Defaults to
“Push the Edit button on the next page”

edit_on_github_skip_regex

When the path to the .rst file matches this regular expression,
no “edit this page on github” link will be added. Defaults to
"_.*".

This extension (and some related extensions) are a port of the
numpydoc extension
written by the NumPy and SciPy, projects, with some tweaks for
Astropy. Its main purposes is to reprocess docstrings from code into
a form sphinx understands. Generally, there’s no need to interact with
it directly, as docstrings following the Astropy Docstring Rules will be
processed automatically.

astropy_helpers.sphinx.ext and sphinx-automodapi includes a few other
extensions that are primarily helpers for the other extensions or
workarounds for undesired behavior. Their APIs are not included here
because we may change them in the future.